Electrostatic precipitator having dual polarity ionizing cell

ABSTRACT

An electrostatic precipitator air cleaner having a novel ionizer cell made up of a plurality of positively charged wire-like ionizer electrodes, a plate-like negatively charged passive electrode positioned between and parallel to each adjacent pair of ionizer electrodes, and a box-like enclosure surrounding the ionizer cell such that the side walls of the enclosure adjacent the outermost ones of the ionizer electrodes form grounded electrically conducting surfaces, a relatively high electrostatic field being produced in the region between the ionizer electrodes and the passive electrodes and between the ionizer electrode and the grounded surfaces. In a preferred embodiment, the ionizer electrodes and passive electrodes are impressed with relatively high voltages of equal but opposite polarity such that the spacing between an ionizer electrode and an adjacent passive electrode is twice the spacing between an ionizer electrode and the adjacent grounded surface.

SUMMARY OF THE INVENTION

The present invention relates generally to improvements in a two stageelectrostatic precipitator air cleaner for removing airborne particulatematerial. The operation of such conventional two stage electrostaticprecipitator air cleaners is well known, and only need be brieflydescribed. In general, airborne dirt and dust particles entering thecleaner under the influence of a blower or other air moving apparatus,are charged to a relatively high positive potential by means of anionizer cell containing a plurality of spaced ionizer electrodes. Thepositively charged particles are then directed to a collecting cell ofthe air cleaner which is made up of a number of alternating grounded andpositively charged collecting plates. The positively charged airborneparticles are repelled by the positively charged plates, and collectedon the grounding plates, where they may later be removed by rapping,washing or the like as is well understood in the art.

The conventional ionizer cell contains a number of parallel spacedwire-like ionizer electrodes oriented transversely to the incomingparticle-laden airflow which are separated by relatively narrow parallelspaced grounded passive electrodes. The electrostatic field formedbetween the charged wire-like electrodes and the grounded passiveelectrodes charge the airborne particles as noted hereinabove. In theusual type of construction, the spaced passive electrodes are supportedfrom each other, and from the electrostatic precipitator air cleanercasing by conductive rods or spacers, which places the air cleanercasing at ground potential. This type of configuration facilitatesattaching the air cleaner to grounded duct work and eliminates shockhazards for personnel operating near the air cleaners.

It has been proposed to increase the collecting efficiency of such aircleaners by increasing the voltage potentials impressed on the ionizerelectrodes in order to produce a higher electrostatic field for chargingthe airborne particles. One important electrostatic precipitator designparameter is corona current per unit length of ionizer electrode. Forany given geometrical shape of the ionizer electrode, such ascylindrical, for example, this current per unit length determines theelectric field and ion density. Provided the air velocity through theionizer cell of the precipitator is held constant, the resultingelectric field strength and ion density determine the charge perparticle. Consequently, by increasing the current per unit length ofionizer electrode, the particle charge may also be increased. However,it has generally been found that for a particular charged ionizerelectrode to grounded passive electrode spacing, the ionizer voltage canonly be increased to a certain point before breakdown or sparkover inthe region between the electrodes occurs causing corona and sparkingwhich can create a fire hazard and excess ozone production. A potentialof 30,000 volts/cm has often been quoted as a typical breakdown voltagefor uniform clean electrodes, although only 3,000 volts/cm is typicallyobtainable in practice. Consequently, there is some limiting current atwhich the corona becomes erratic so that sparkover occurs.

Since it has been found that all of the ozone is produced at the ionizerelectrode wire, increasing the impressed ionizer voltage as well as theionizer electrode to passive electrode spacing permits more air to flowfor the same amount of ozone produced. Usually, when the spacing of thecharged and grounded ionizer electrodes is increased, the ionizerelectrode wire diameter can also be increased resulting in a more ruggedconstruction. Consequently, this also increases the collectingefficiency of the air cleaner since higher electrostatic fields areproduced for charging the airborne particles.

Unfortunately, it has generally been found that power supplies necessaryto produce high single polarity positive voltages for producing anincreased electrostatic field between the ionizer electrode and thegrounded passive electrode are impractical from a cost and complexitystandpoint. However, I have found that the necessary increasedelectrostatic field strength can be produced by impressing the ionizerelectrodes with a conventional high voltage positive potential, andimpressing the passive electrodes with a high voltage negativepotential, rather than referencing the passive electrodes to ground asin conventional electrostatic precipitator air cleaners. Thisconstruction permits the use of simple, low cost conventional highvoltage power supplies, and avoids other problems which may occur whenvery large single polarity voltages are used.

Using this technique, the electrostatic precipitator air cleaner of thepresent invention provides improved operation and performance over knownelectrostatic precipitators using single polarity ionizer powersupplies. Furthermore, in a preferred embodiment, the outermost or endpassive electrodes, which may form a part of the air cleaner casing, areelectrically grounded and insulated from the negatively charged passiveelectrodes to insure a safe, potential-free enclosure surrounding theair cleaner. The outermost ionizer wire electrodes which are charged toa relatively high positive DC potential, are spaced the conventionaldistance from the grounded end plates, such that the usual electrostaticfield is produced in this region. The adjacent passive electrode,however, is charged to a relatively high negative DC potential, and isspaced from the ionizer wire by twice the usual distance to producesubstantially the same voltage gradient between the charged passiveelectrode and the ionizer wire that exists in conventional electrostaticprecipitator air cleaners between the ionizer wire and the groundedpassive electrode. For example, in the preferred embodiment illustratedand described, where the ionizer wire electrodes and the passiveelectrodes are impressed with voltage potentials of the same magnitudebut opposite polarities, the distance between the charged collectingplates and the ionizer wires will be twice the distance measured betweenan ionizer wire and a grounded passive electrode or end plate. Thisarrangement results in a construction where only charged passiveelectrodes are utilized in the interior of the ionizing cell, resultingin substantially the same voltage gradient being produced as inconventional electrostatic precipitator ionizer cells, but withsignificant savings in materials and simplification of construction.

Further details of the invention will become apparent from the detaileddescription which follows.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a rear view, partially in schematic form, of a typical priorart electrostatic precipitator air cleaner illustrating the outlet endof the ionizer cell.

FIG. 2 is a fragmentary cross sectional view taken along section line2--2 of FIG. 1.

FIG. 3 is a fragmentary cross sectional view, partially cut away, takenalong section line 3--3 of FIG. 1.

FIG. 4 is a rear elevation view, partially in schematic form, of theelectrostatic precipitator air cleaner of the present invention showingthe outlet end of the ionizer cell.

FIG. 5 is a fragmentary cross sectional view taken along section line5--5 of FIG. 4.

FIG. 6 is a fragmentary cross sectional view, partially cutaway, takenalong section line 6--6 of FIG. 4.

DETAILED DESCRIPTION

FIG. 1-FIG. 3 illustrate a typical prior art electrostatic precipitatorair cleaner, shown generally at 1 which includes an ionizer cell 2having an inlet end 3 for accepting particle laden air, and an outlet 4which communicates with the inlet end 5 of a collecting cell 6. Ingeneral, airborne dirt and dust particles contained in the airstreammoved through the precipitator by air moving means (not shown) arecharged in ionizer cell 2 to a relatively high positive potential. Thepositively charged particles are then directed to the collecting cell 6of the air cleaner 1 where the particles are collected on collectingplates for subsequent removal by cleaning means such as a rapper orwashing mechanism (not shown).

In the conventional electrostatic precipitator air cleaner 1, collectingcell 6 comprises a plurality of parallel spaced collecting electrodes,one of which is shown at 7, interleaved with parallel spaced groundedcollecting electrodes, one of which is shown at 8. The positivelycharged particles passing through collecting cell 6 are repelled bypositively charged plates 7 and collected on grounded collecting plates8. Collecting cell 6 may be contained within a box-like electricallyconducting enclosure 9 which may also be grounded to facilitateconnection to an air duct or the like (not shown). Furthermore, the sidewalls 10 of enclosure 9 may form a pair of grounded collectingelectrodes.

The ionizer cell 2 of the conventional electrostatic precipitator aircleaner 1 comprises a box-like enclosure 11 which is adapted to matewith the front edge of collecting cell 6 to form a continuous duct-likeair passageway through the air cleaner. Contained within enclosure 11are a number of narrow parallel spaced electrically conducting passiveelectrodes, one of which is shown at 12, which are electricallyconnected and supported near their top and bottom edges by electricallyconducting rod-like spacing members 13 and 14. The ends of spacingmembers 13 and 14 are supported by and electrically connected to endplates 15 of enclosure 11, which may be grounded as at 16, therebyplacing all of passive electrodes 12, as well as enclosure 11, at groundpotential. This arrangement facilitates attaching the ionizer cellenclosure 11 to enclosure 9 of collecting cell 6, as well as to othergrounded air ducts, not shown.

The ionizing electrodes are formed by a plurality of parallel spacedthin electrically conducting wires, one of which is shown at 17,interleaved between adjacent passive electrodes 12. The ends of eachionizer wire 17 are connected to parallel spaced transversely extendingelectrically conducting support bars 18 by means of tension springs 19which urge the ends of ionizer electrode wire 17 outwardly to maintainthe proper tension. Support bars 18 are electrically insulated fromionizer cell enclosure 11 by means of electrically non-conductingstand-off supports 20 attached between support members 18 and the upperand lower front flanges 21 of enclosure 11.

Electrostatic precipitator 1 also includes a power pack 22 whichsupplies a relatively high positive DC potential voltage, on the orderof 12 KV for a typical air cleaner, to support bars 18 in order tocharge ionizer wire electrodes 17. In many instances, the same voltagewill be utilized to charge collecting electrodes 7 of collecting cell 6.

It will be observed that in this typical arrangement, only a singlepolarity power supply is utilized, and the ionizer electrode and passiveelectrode spacing is constant in ionizer cell 2. Generally, the spacingbetween the ionizer electrodes 17 and the passive electrodes 12 will besuch as to create the maximum voltage gradient while avoiding sparkoverconditions. It will further be observed that the enclosure formed byionizer cell enclosure 11 and collecting cell enclosure 9 is grounded inorder to facilitate connecting the air cleaner unit to grounded ductwork or the like.

The improved electrostatic precipitator air cleaner of the presentinvention is illustrated generally at 100 in FIG. 4-FIG. 6. In general,elements in the embodiment of FIG. 4-FIG. 6 corresponding to elements inthe prior art embodiment described hereinabove will be given the samedesignation. For example, collecting cell 6 may be constructed in thesame manner as described hereinabove, and will include a box-likeenclosure 9, generally constructed of an electrically conductingmaterial, having an inlet end 5 for connecting collecting cell 6 to theionizer cell 200 of the present invention.

As illustrated in FIG. 4-FIG. 6, ionizer cell 200 comprises a generallybox-like enclosure 11 similar to that described hereinabove inconnection with the embodiment of FIG. 1-FIG. 3, formed by a pair ofspaced upstanding plate-like electrically conducting end walls 15, andupper and lower front flange plates 21. Enclosure 11 may be grounded asat 16 to facilitate connecting the ionizer cell to duct work or thelike, not shown.

Contained within enclosure 11 are a plurality of parallel spaced narrowpassive electrodes, one of which is shown at 212, of roughly the samesize, shape and construction of passive electrodes 12 of a conventionalelectrostatic precipitator air cleaner. The outermost passive electrodes212 are supported from end plates 15 by a pair of spaced electricallynon-conducting spacing members 214a which insure that the outermostpassive electrodes 212 are electrically isolated from enclosure 11.

Interspersed between the outermost passive electrodes 212 are aplurality of similarly configured passive electrodes 212 which arepositioned in parallel relationship with the outermost passiveelectrodes, and spaced therefrom by parallel spaced electricallyconducting support members 214b, thereby insuring that all passiveelectrodes 212 will be at the same electrical potential.

As illustrated in FIG. 4, ionizer cell 200 includes a plurality ofspaced parallel thin wire-like ionizer electrodes 17 interleaved withpassive electrodes 212 and extending between a pair of spaced paralleltransversely extending support bars 208 electrically insulated fromionizer cell frame 11 by stand-off insulators 20. Ionizer electrodes 17are held under the proper tension by means of tension springs 19 asdescribed hereinabove with respect to the embodiment of FIG. 1-FIG. 3.The spacing of passive electrodes 212 and ionizer electrodes 17, whichforms an important feature of the present invention, will be explainedin more detail hereinafter.

Ionizer wire electrodes 17 are charged to a relatively high positive DCpotential by means of positive power supply 22, the output of which isconnected to one of support bars 208. Passive electrodes 212 are chargedto a relatively high negative DC potential by means of negative powersupply 222, the output of which is connected to one of electricallyconducting spacing members 214b. If desired, a single power pack havingdual voltage outputs may be utilized in lieu of separate power supplieshaving opposite polarities.

It will be understood that this construction produces an arrangementwhere relatively high electrostatic fields are produced in the regionbetween end plates 15 and the outermost ionizer wires 17, and theregions between ionizer wire 17 and negatively charged passiveelectrodes 212. As illustrated in FIG. 4, ionizer wires 17 andnegatively charged passive electrodes 212 may be impressed with voltagesof the same magnitude, but opposite polarity, for example ±12 KV. Underthese conditions, the outermost ionizer wires will be spaced from theirassociated end plates 15 approximately the same distance as in theconventional electrostatic precipitator 1 illustrated in FIG. 1-FIG. 3in order to produce the required voltage gradient between these ionizerwires and their associated end plates. In addition, passive electrodes212 will be spaced from their adjacent ionizer wire electrodes 17 adistance equal to twice the spacing between the associated ionizer wire17 and passive electrode 12 in the conventional electrostaticprecipitator air cleaner 1. This arrangement insures that the voltagegradient thus produced in the regions between ionizer wire electrode 17and passive electrodes 212 will be substantially the same as the voltagegradient produced between the outermost ionizer wire electrode 17 andend plates 15, even though the actual potential difference between theionizer wire 17 and the passive electrodes 212 is twice as great as thepotential difference between the outermost ionizer wires 17 and the endplates 15. In other words, the positioning means formed by support bars208 position each ionizer wire 17 within ionizer cell 200 such that atleast one of the ionizer wires is unequally spaced with respect to theadjacent grounded end plate while insuring that the voltage gradientsproduced between each of the ionizer wires and the adjacent passiveelectrode are substantially the same. It will be understood that by"unequally spaced" is meant that the ionizer wire 17 is not centeredbetween its adjacent passive electrode 212 and the associated end plate15.

It will be further understood that one of the important features of thepresent invention is the positioning of the ionizer wires on supportbars 208 such that the voltage gradient between the ionizer wire and theadjacent end plate is substantially the same as the voltage gradientbetween an ionizer wire and an adjacent charged passive electrode 212.In the preferred embodiment described hereinabove where end plates 15are electrically grounded, and charged passive electrodes 212 andionizer wire 17 are impressed with relatively high DC voltage potentialsof equal magnitude but opposite polarity, the ionizer wires will bepositioned such that the distance between one of the ionizer wires andan adjacent passive electrode is twice the distance measured between anionizer wire and the adjacent grounded end plate. For example, with endplates 15 grounded, and ±12 KV supplied to the ionizer wires and chargedpassive electrodes, respectively, and an assumed charged passiveelectrode to ionizer wire spacing of three inches, a voltage gradient of8 KV per inch will be produced in the region between the ionizer wireand the adjacent collecting plate. Consequently, in order to produce thesame voltage gradient in the region between the ionizer wire and anadjacent grounded end plate 15, a spacing of 1.5 inches will benecessary.

However, the inventive principal described and illustrated in thepreferred embodiment hereinabove may be extending to electrostaticprecipitator air cleaner constructions utilizing different chargingmeans. For example, the polarities of the charging means or power packs22 and 222 may be reversed so that a relatively high negative DC voltageis applied to the ionizer wires and a relatively high positive DCvoltage is applied to the charged passive electrodes 212. Furthermore,while for purposes of an exemplary showing, the output voltage producedby power packs 22 and 222 have been described as equal and of oppositepolarity, these voltages may be made unequal as desired with acorresponding change in the spacing between the outermost ionizerelectrodes and end plates 15 such that the same voltage gradient isproduced between the outermost ionizer wires and end plates 15 as isproduced in the region between the ionizer wires and the adjacentcharged passive electrode. For example, in the particular constructiondescribed hereinabove where grounded end plates 15 and an assumedionizer wire to charged passive electrode spacing of three inches areutilized, a positive DC voltage produced by power pack 22 of +12 KV anda negative DC potential of -6 KV produced by power pack 222 will resultin a voltage gradient of 6 KV per inch in the region between the ionizerwire and the adjacent charged passive electrode. This situation requiresthat the ionizer wire be spaced from the adjacent grounded end plate 15by a distance of two inches.

The electrostatic precipitator 100 of the present invention may befurther modified by utilizing charging voltages of only one polarity,such that the voltage applied to ionizer wires 17 is at a greaterpositive potential than the positive voltage applied to passiveelectrodes 212. For example, in the case where grounded end plates 15and an ionizer wire to charged passive electrode spacing of three inchesare utilized, with a voltage potential of +12 KV produced by power pack22 and a voltage potential of +6 KV produced by power pack 222, avoltage gradient of 2 KV per inch will be produced in the region betweenthe ionizer wire and the adjacent passive electrode so that the ionizerwire to end plate spacing will be six inches.

The electrostatic precipitator air cleaner of the present invention maybe further modified by charging end plates 15 to a specified voltage sothat the end plates also act as charged passive electrodes. In thissituation, the passive electrodes and ionizer wires will be equallyspaced as in the arrangement shown in FIG. 1-FIG. 3. However, thisembodiment may have the drawback that additional insulating means mustbe utilized when connecting the electrostatic precipitator to anexisting grounded air duct or the like.

Finally, it is contemplated to be within the scope of the presentinvention to charge various ones of the ionizer wires to differentvoltages, and/or various ones of the charged passive electrodes todifferent voltages. For example, for a construction where end plates 15are grounded the outermost ionizer wires 17 are provided with thevoltage potential of +12 KV, the inner ionizer wires 17 are providedwith a voltage potential of +6 KV, the passive electrodes 212 areprovided with a voltage potential of -12 KV, and an ionizer wire topassive electrode spacing of three inches is utilized, all resulting ina voltage gradient in the region between the ionizer wires and thepassive electrodes of 6 KV per inch, an ionizer wire to end platespacing of two inches will be required.

This arrangement leads to several important advantages over knownelectrostatic precipitator air cleaners. For example, a significantimprovement in reducing back ionization is realized which results inlower ionizer currents under conditions of heavily particle coatedcollector plates. In addition, fewer ionizer wires and passiveelectrodes are necessary, leading to a reduction in overall material andassembly costs, as well as possible reduction in the required size ofthe power supply. Since the power requirements have been reduced, asignificant energy savings is also realized, and a single power supplycan be used to energize several different electrostatic precipitatorunits.

It will be understood that various changes in the details, materials,steps and arrangements of parts, which have been herein described andillustrated in order to explain the nature of the invention, may be madeby those skilled in the art within the principal and scope of theinvention as expressed in the appended claims.

Embodiments of the invention in which an exclusive property or privilegeis claimed are as follows:
 1. A two-stage electrostatic precipitator aircleaner for removing particles from an airstream laden with saidparticles comprising an ionizer cell for producing a plurality ofrelatively high electrostatic fields for charging said particles and acollecting cell positioned downstream from said ionizer cell forcollecting said particles, said ionizer cell comprising:a plurality ofthin electrically conductive spaced parallel wire-like ionizerelectrodes positioned across the inlet to said ionizer cell; means forcharging said ionizer electrodes to a first relatively high DC voltage;an electrically conducting plate-like passive electrode positionedbetween and parallel to each adjacent pair of said ionizer electrodes;means for charging said passive electrodes to a second relatively highDC voltage such that a relatively high electrostatic field is createdbetween said ionizer electrodes and said passive electrode; and abox-like enclosure surrounding said ionizer cell, the side walls of saidenclosure adjacent the outermost ones of said ionizer electrodes forminggrounded electrically conducting surfaces, a relatively highelectrostatic field being produced between the outer ones of saidionizer electrodes and said surfaces.
 2. The electrostatic precipitatorair cleaner according to claim 1 including means for positioning saidionizer electrodes such that the voltage gradients produced between eachof said ionizer electrodes and an adjacent passive electrode and betweeneach of said ionizer electrodes and an adjacent one of said groundedsurfaces are substantially the same.
 3. The electrostatic precipitatorair cleaner according to claim 2 wherein said first and second voltagesare the same in magnitude but opposite in polarity, and said positioningmeans spaces said ionizer electrodes twice the distance from saidpassive electrodes as from said grounded surfaces.
 4. The electrostaticprecipitator air cleaner according to claim 3 wherein said first voltageis of positive polarity.